For many applications, it is necessary to measure and display a person's body response, such as his or her heartbeat. In particular, in exercise and fitness training, it is often the situation that a person wishes to measure his or her heartbeat in order to achieve the maximum benefits of the exercise without the danger of increasing the heartbeat to a rate where adverse effects could occur. Of course, such measurements are also useful for many health applications such as biofeedback and exercise programs where the participants only mildly exercise and do not approach greatly elevated heart rates. Over the years, various types of equipment have been marketed for the measurement of heart rate, such instruments being popular in a wide variety of applications extending from all forms of exercise to biofeedback. Continuous accurate heart measurement is an important part of all aerobic exercise and rehabilitation programs and for this reason many types of apparatus have been commercially available for personal use by individuals and in fitness clubs, etc. Some of this equipment includes heart rate monitors that are used to control the intensity of the workout based on the user's measured heart rate. As will be discussed later, the problem of providing a good monitor necessarily affects the quality of an exercise program that is response to a measured heart rate.
Some of the most popular heartbeat monitor designs use wireless data transmission from a sensor-transmitter unit to a display unit. This type of design allows optimal and flexible positioning of both units while not limiting a person's freedom of movement. Unfortunately, the increasing popularity of heart measurement, and therefore the use of these heart monitors, has demonstrated the limitations of currently available designs. An example is the recurring interference effects brought about when a person wearing a heart monitor is in close proximity to another person wearing another heart monitor. These people run the risk that their individual monitor readings are influenced by the monitor worn by the other person. Further, it is equally frustrating for a person wearing a heart monitor to find that electromagnetic equipment of all types, such as exercise equipment, power lines etc. will create electromagnetic fields that interfere with the successful transmission of his or her heartbeat, thereby causing an erratic display which is uncorrectable without moving away from the interfering exercise equipment, power lines, etc.
Various types of wireless measuring methods have been proposed. Some of these are based on radio waves while others use a magnetic proximity field. Most of these prior techniques transmit an analog ECG signal of a person. However, as noted, these prior techniques and apparatus are not simultaneously usable by several persons in close proximity to one another or by person who are using such apparatus in close proximity to electrical or electronic equipment. In such cases, the reliability of transmission of heartbeat is significantly reduced with the result that a continuous and accurate monitoring of the heartbeat is no longer possible. As is readily appreciated, this lack of reliability is a problem for anyone using the monitor and is especially disconcerting to a person who is exercising to a level where his or her heartbeat is close to the maximum desired for that person.
Examples of some prior art monitors include U.S. Pat. No. 4,625,733; U.S. Pat. No. 4,425,921; U.S. Pat. No. 3,212,496; and U.S. Pat. No. 3,949,388. The first of these describes a heartbeat monitor using a magnetic proximity field as a basis for analog wireless transmission, where a particular arrangement of magnetic coils is used in the transmitter and the receiver units.
U.S. Pat. No. 4,425,921 describes a portable heartbeat monitor which can be used to check either pulse rate or heart rate using separate sensors for detecting heartbeat and pulse beat. The apparatus shares a common indicator for displaying the heartbeat rate or pulse beat rate depending upon a switch means for connecting either of the sensors to a microcomputer. Analog signals are used in this monitor, which does not use wireless transmission between a transmitter and receiver.
U.S. Pat. No. 3,212,496 describes an apparatus for simultaneously measuring ECG, respiration rate, and respiration volume. A pair of electrodes on or in a person's body have current passed therebetween and sense an impedance change and a heartbeat voltage. A frequency modulated signal can then be telemetered to a receiving and display unit.
U.S. Pat. No. 3,949,388 describes a portable apparatus that can be used for analog biomedical telemetry, and is particularly adapted for use in a hospital where each sensor-transmitter unit is used on a single patient and will not normally be used on another patient. The transmitter is designed to produce a very narrow frequency spectrum where a steady pulse rate accurately represents the measured temperature of the patient. In order to avoid interference from adjacent units, the receiver unit is located within only a few feet of the transmitting unit. Further, a very low power continuously sending transmitting unit is used so that only the closest receiver will detect the analog signal. This avoids the possibility that the receiver will pick up signals from another transmitter. Thus, the selectivity of the receiver is based on its close proximity to the associated transmitter unit, not on any circuitry which would prevent interference by a transmitter broadcasting a high power signal, even though such interfering transmitter may be far away. Further, the frequency range intended for operation is selected to be very narrow. As noted in this patent, frequency sweeping can occur due to saturation of a transistor in the oscillator circuit. In order to prevent this undesirable frequency sweeping, an isolating impedance is used in the circuit design to prevent feedback current of the type which causes the transistor saturation.
U.S. Pat. No. 5,157,604 describes a hospital monitoring system in which many patient transmitter units are coupled to a central station. Wireless transmission of a signal including an identifier and heartbeat data occurs from each patient unit to the central station. Each patient unit transmits on its own frequency so there will be no interference between the patient units. The responses of the patient units are time multiplexed, since these units respond to the central station only in response to the receipt of a timing signal from the central station. Error detection and correction of an incorrect heartbeat due to faulty transmission is not mentioned.
In the prior art monitors for measuring and displaying heartbeat, it is usually not possible to provide a technique and apparatus for determining if the received signal in the display unit is from the properly associated transmitter unit or is instead from another transmitter unit. Further, if there are errors occurring in the data representing the heartbeat, such as missing portions of the signal due to interference from outside sources, the display in these prior monitors will either indicate a wrong value, not indicate heartbeat, or maintain the previous reading without making the user aware of the problem. In these prior art monitors, there is no way to account for transient errors in heartbeat which are momentarily caused but which do not necessarily render inaccurate the later readings of heartbeat. If these prior art monitors are used to control exercise equipment, there is a problem due to interference from the motors in the equipment and also from other monitors on equipment that is closely located to the user's exercise equipment.
It is therefore a primary object of the present invention to provide an improved technique and apparatus for monitoring and displaying a biomedical function (body response) such as heartbeat, wherein the above-described problems are addressed and corrected and to provide exercise equipment using this improved apparatus.
It is another object of the present invention to provide exercise equipment using an improved personal use heartbeat monitor which automatically rejects interfering signals from sensor-transmitter units other than the one with which the display unit is properly associated.
It is another object of the present invention to provide a heartbeat monitor in which the presence of transient errors in the signal representing the heartbeat does not render inaccurate the heartbeat displayed to the person wearing the monitor, where this monitor is used to control exercise equipment in accordance with the person's instantaneous heart rate.
It is another object of this invention to provide a wireless heartbeat monitor which can be easily worn by a person engaged in all forms of physical exercise, and which will nonetheless provide accurate measurement of the person's heartbeat even in the presence of other heartbeat monitors and/or electrical or electronic equipment in which components of the monitor are located.
It is another object of the present invention to provide exercise equipment in which a part of a person's ECG signal is digitally encoded for wireless transmission to a receiver-display unit located in the exercise equipment, where the coding allows a receiver-display unit to identify the encoded digital signal as having been sent from a particular sensor-transmitter unit.
It is another object of the present invention to provide exercise equipment using a heartbeat monitor which will automatically change the frequency range over which signals representing the heartbeat are wirelessly sent from a sensor-transmitter unit to a receiver-display unit, the transmission frequency being changed in response to the occurrence of errors in the received signal.
It is a further object of this invention to provide a technique and apparatus for monitoring heartbeat where the monitor is used in exercise equipment without adversely affecting the accuracy of the data displayed to the person using the monitor.
It is another object of this invention to provide improved exercise equipment for isolating monitor signals relating to a biological function, such as heartbeat, wherein the monitored signals are digitally encoded to provide user identifiers that are wirelessly transmitted.
It is a still further object of this invention to provide automatic transmission error detection and correction in a wireless biological response monitoring system used to control exercise equipment in accordance with a user's biological response.